Power plants that operate on the Rankine cycle utilizing an organic fluid are well known. In such plants, the organic fluid is vaporized in a vaporizer or boiler using heat from burning fuel, a geothermal source, or an industrial process; and the vaporized working fluid is expanded in a turbogenerator for producing power and heat depleted working fluid which is condensed in an air or water cooled condenser to produce liquid working fluid that is returned by a pump to the vaporizer.
The working fluid is selected to have the proper thermodynamic properties for the cycle, such as heat capacity, stability at the working temperatures, etc., and to be compatible with the metals used in conventional turbine installations. In addition, the working fluid must exhibit good lubricating properties because, conventionally, the turbine, as well as the generator coupled thereto, are in a hermetically sealed canister within which liquid working fluid from the condenser is used as a lubricant.
Generally, the working fluid will be a hydrocarbon, such as pentane, or hexane, or an isomer thereof such as isopentane or isohexane. Other well defined chemicals are also used. But in each case, the working fluid is a commercially available, commercially pure material that has well defined and known properties that are utilized in the design of the hardware of the power plant. Sometimes, mixtures of hydrocarbon fluids are used to take advantage of special properties of the mixtures as described in U.S. Pat. No. 3,842,593 where a specific mixture of hydrocarbons provides the power plant with the capability of operating under ambient conditions that would not permit use of a pure material.
Because the manufacturer of an organic fluid Rankine cycle power plant must guarantee that it will produce a predetermined electrical output from a source producing a predetermined amount of heat per unit time, the selected working fluid, or mixture of fluids, must have well defined physical properties. That the chosen fluid or fluids will have these properties is ensured by utilizing commercially pure fluids that conform to international standards. These fluids are readily available in most parts of the world; but there any many places in the world where suitable pure fluids are exorbitantly expensive, or when used in a power plant environment create governmental regulatory problems because of lack of historical precedent for their use under such conditions.
Some organic fluids theoretically capable of being used in a power plant environment are considerably less expensive, or more readily available, than those usually employed in power plants, but these fluids are usually mixtures whose pressure-volume-temperature characteristics are unknown, or vary widely from place to place and from time to time. As a consequence, the designer of the power plant can never be certain that such fluids will perform in a power plant in the predictable ways that a pure fluid whose properties are established will perform. For example, the motor fuel gasoline is one of the most ubiquitous fluids in the world, from highly industrialized countries to the poorest third world countries. In some countries, the availability of gasoline exceeds that of water, and public acceptance of and government regulations on the storing and use of gasoline are well established as compared with many of what seem to lay persons as the exotic organic fluids that have been proposed for Rankine cycle power plants. However, the use of gasoline or other hydrocarbon comprising a plurality of fractions is not a viable choice for an organic fluid Rankine cycle power plant because of the uncertainty of the thermodynamic properties of a particular batch of gasoline in a particular place in the world at a particular time. The designer can not know beforehand the thermodynamic properties of a batch of gasoline that will be delivered to a plant at start-up or later as make-up working fluid; and thus, his design can not take into account the possible variations that can occur. As a consequence, gasoline is rejected out of hand by a designer.
It is an object of the present invention to provide a method of and means for using well known, readily available, acceptable, commercial organic fluids, such as gasolines, in a Rankine cycle power plant regardless of the possible variations in thermodynamic properties from time to time and from place to place.